The present invention relates to a minimally invasive apparatus and method for preparing the articular surface of the patella to receive a patellar implant without everting the patella.
Several studies have shown that minimizing the patellar eversion throughout a resection procedure can produce better and faster functional outcomes. Known methods and surgical tools for preparing the articular surface of the patella to receive a patellar component thereon all require eversion of the patella from its anatomically correct position at some point during either resecting the patella for implant fixation, or securing a patella component to the resected patella.
Prior art devices for preparing the patella for receiving a patellar implant are well known to those skilled in the art. It is known in the art to prepare the patella during total knee replacement by everting, i.e. rotating the articular surface anteriorly, the patella approximately 180°, or with newer minimally invasive techniques between 45° and 90°. Patella clamps may be used to clamp the anterior and articular surfaces of the patella before resecting the articular surface of the patella. Additionally, some patella clamps may require fixation pegs or keels to engage the patella before everting it to a desired angle. Common methods to remove bone from the articular surface of the patella include saw resection or milling/planar systems. The removal of bone in either of these systems may provide a flat, stable platform to support, but not secure, a prosthetic patellar component.
For example, Waddell, in U.S. Pat. No. 6,174,314 teaches a patella resection guide and method of resurfacing the patella in situ. In this teaching, after adjustments in a resection guide are made, the patella is cut while in its non-everted position. For non-eversion of the patella to occur during resection, the Peterson device requires a flat or angled saw cut to be made through the resection guide.
U.S. Pat. No. 6,159,246 relates to a surgical method and tool for preparing a patella of the knee joint. Here, a method and device are provided which enable the preparation of a natural patella for accepting a patella implant. The patella is first held with a patella holder or clamp, then everted, and then shaped by means of a bone shaping element.
Other patella resection guides may not evert the patella if a saw is used to cut a desired amount of the articular surface of the patella. Generally when the patella is milled or reamed the patella must be everted at some degree during resection. Further, in order to secure a patella component in any of the prior art systems, at least some eversion of the patella must occur during either resecting the patella or securing a patella component to the resected patella.
Many patella resection guides are known, each having various designs to clamp and mill/saw the patella. Such designs are shown in prior U.S. Pat. Nos. 5,716,360; 5,575,793; 5,536,271; and 5,129,907. Improvements in patella resection guides allowing the patella to be reamed to receive an implant thereon without everting the patella during the reaming step are desirable. A minimally invasive method of preparing the patella to receive an implant thereon without everting the patella is desirable especially where only two small incisions through the skin of the knee are made. Specifically, the articular surface of a patella may be prepared to receive an implant thereon without everting the patella if a medial or lateral parapatellar incision is made through the knee capsule adjacent the patella to gain entry into the knee joint, and another anterior midline incision is made through the skin of the knee down to the anterior surface of the patella bone. More generally, the two incisions may be a medial or lateral parapatellar incision and a small anterior midline incision made above the centerline of the patella. Currently, there is no system that allows the entire patella preparation and implantation of a patellar component to be performed by reaming without everting the patella.